Process for purification of pentaerythritol tetranitrate



Patented Nov. 7, 1933 1,933,754 7 V PROCESS FOR PURIFTCATIONQOF, ,PFENP 'rAEaYTHRiToL TETRANITRATE Thomas Ramsay Paterson, West Kilbride, Scotland, assignor to Imperial Chemical lndustries Limited, a corporation'of- Great Britain.

No Drawing. Application May 5, 1932, Serial No. 609,552, and in Great Britain May 13,

. 6 Claims. (crest- 144) water and having relatively high boiling points, 7

in which case. the final traces of solvent are removed from the compound by steam distillation.

The manufacture of solid explosive organic nitrocompounds, or organic nitrates, which are .the substances covered by my invention, involves the nitration of the raw material with nitric acid, either alone or together with sulfuric acid. The solid nitration product is removed from the spent acid by filtration, decantation or other method, and is washed with water, and frequently with a dilute alkaline solution, for example ammonia, or anaqueoussolution of sodium carbonate. The product obtained aboveoften contains an undesirable amount of impurities, particularly impurities of an acid nature due to the inclusion of foreign acidic material within the crystals. The presence of such impurities has an undesirable efiect on the stability .of the explosive product, as shown by various heat tests, etc.

The object of my invention is to provide an improved process for the purification of pentaerythritol tetranitrate, trinitrotoluene, tetryl and other normally solid organic explosive compounds. A further object is to provide a process for the purification of such compounds us-- ing a solvent giving oif no considerable amounts of inflammable vapors, at ordinary temperatures, to form explosive mixtures with air. A still further object is to provide a process using a solvent immiscible with water but capable of removal from the purified material by distillatlon with steam. Other objects will be apparent after free acid and any insoluble impurities.

have been removed therefrom. The free acid may be removed by washing with water or alkaline solutions, and before or after removal of the insoluble impurities by filtration or other means. Whilevarious solvents are adapted for explosive compound being purified.

fully.

such use, for example high boiling point 'alie phatic hydrocarbons, aniline, aromatic hydro? carbons such asxylenejandflike compounds, I prefer to usenitrobenzene. H K

- The solubility of pentaerythritol tetranitrate, for example, in nitrobenzene is such as to make the latter solvent a desirable one for use. Since this solvent has'a high boiling point, the vapor pressure is low at ordinary temperatures, and explosive mixtures are ,not. formed with air; After. purification of the pentaerythritol,tetranitrate by nitrobenzene and. removal of the'im purities by filtration, the nitrobenzene maybe removed from the explosive compound by steam distillation. f ,My process, as outlined above, may be applied to any one of a' number ofnormallysolid organic explosive compounds, for example tetryl, trinitrotoluene, trinitrobenzene, trinitronaphthalene tetranitroaniline, pentaerythritol tetranitrate etc..

A further improvement in my process may bev introduced by the use of a mild alkali dissolved ammonia or a dilute sodium carbonate solution may be used. Thus when the organic solvent is steam distilled off it may be conveniently done in presence of a dilute alkaline solution. If desired, ammonia may be introduced into the distillation liquid by addition to the steam entering the vessel. The use ofthe above alkali insures the complete elimination of acidity from the By way of illustration the following specific example is given to illustrate my invention more Twenty-five lbs. of moist crude pentaerythritol tetranitrate, containing 5 lbs. of water, are brought into solution inlOO lbs. of nitrobenzene by agitation at a somewhat elevated temperature. The hot mixture is filtered to remove the solid undissolved impurities, and the filtrate is then steam distilled, togetherwith a considerable quantity'of a warm.1% sodium carbonate solution, for example. The distillation is continued until the condensate is free from nitrobenzene. At this time the aqueous solution should still be. alkaline. I I

With the removalof the nitrobenzene from the distillation vessel, theapurified pentaerythritol tetranitrate separates' outf The crystals are filtered, washed, and dried at 100 C.

Pentaerythritol tetranitrate, produced according to the above process, possesses a high degree of purity and shows high stability when tested by the usual heat tests.

The method of purification described heretofore has many advantages over the acetone purification process generally used according to the prior art. Acetone is a Very volatile solvent giving off inflammable vapors, so that the use of hot acetone as a purifying agent adds a fire risk to the process. In addition, 'there'is a loss of solvent by evaporation during thefiltration of the solution from impurities, whichrfrequently causes clogging of the filter because of premature crystallization of the explosive compound.

Moreover, such crystals prematurely formed are not sufiiciently pure and must be subsequently redissolved. g

A further advantage in my process is that the solvent used is obtained free from waterafter the steam distillation, and can be used subse-' quently Without further treatment. In the case of acetone, however, considerable difficulty is in-v volved' in separating theac'etone from the water and obtaining a'solution sufficiently concentrated for further use in'the process; While I have described my invention in the foregoingwith particular reference to pentaerythritol tetranitrate, it shouldbeunderstood' that it applies also to processes for purifying other organic explosive compounds, such as for example trinitroben zene, trinitrotoluene, tetryl; trinitronaphthalene, tetranitroaniline, etc.' It should be understood also that other compounds than 'nitrobenzene may be used as purifying'agents, the only requirement being that they have solvent power for the explosive compounds, that they be notmiscible. With water, and that-they have an elevated boiling Point, above 100 C.

I claim: r 1. The i process of purifying pentaerythritol t'etranitrate, which comprises crystallizing said compound from nitrobenzene.

taerythritol tetranitrate by distillation with steam, said steam distillation being carried out in the presence of an alkaline reagent.

4. The process of purifying pentaerythritol tetranitrate comprising the crystallization of said compound from nitrobenzene, the nitrobenzene being subsequently separated from the pentaerythritol 'tetranitrate by distillation with steam, said steam distillation being carried out in the presence of ammonia. r

5. The process of purifying pentaerythritol tetranitrate obtained by nitratingpentaerythritol, which comprises treating it with'a solvent which is substantially immiscible with water,

which has'a higher boiling point than water and which is volatile in steam, and isolating solid pentaerythritol tetranitrate' from its solution in the said solvent afterfree acid-and any insoluble impurities have been removed therefrom.

6. The process of purifyingpentaerythritol tetranitrate obtained by nitrating pentaerythritol; which comprises treating it with a solvent Which. is substantially immiscible with Water,

whichhas a higher boiling'point than water and' which is volatile in steam, removing any insolua ble impurities'from the solution of pentaerythrito l tetranitrate, and subjecting the said solution to steamdistillation in the presence of a dilute aqueous alkaline solution.

THOMAS 'RAMsA ,PATERSON. 

